US2859282A

US2859282A - Communication switching network

Info

Publication number: US2859282A
Application number: US617060A
Authority: US
Inventors: Kermit S Dunlap; Jeremy P Taylor
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1956-10-19
Filing date: 1956-10-19
Publication date: 1958-11-04
Anticipated expiration: 1975-11-04
Also published as: FR1179110A; DE1034707B; BE561192A; GB850211A

Description

Y- 1958' 2 K. s. DUNLAP ETAL 2,859,282

COMMUNICATION SWITCHING NETWORK Filed Oct. 19, 1956 0 PULSE SOURCE K. S. DUNLAP INVENTORS J R TAYLOR lmy w ATTORNEY United States Patent F 2,859,282 COMlVIUNICATION SWITCHINGNETWORK Kermit S. Dunlap, Madison, N. J., and Jeremy P. Taylor,

Menlo Park, Califi, assignors to Bell Telephone. Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 19, 1956, Serial No. 617,060-

Claims. (Cl. 179-18) This invention relates to switching networks and,

more particularly, to such networks for use in telephone distribution systems whereina path is established through the distribution network on conduction through a selected number of switching devices operable on application of suitable marking potentials to the network and. across the switching devices of the network, which devices are referred to as crosspoints of the switching network.

In Patent 2,684,405, issued July 20, 1954, to E. Bruce,

and H. M. Straube, there is disclosed a selective switching network for a telephone system in which a plurality of gas tubes are connected together to-define individual paths between any one of a number of input terminals.

to which may be connected telephone subscribers and any one of a number of output terminals which may be trunks "2,859,282 rate-med Nov. '4, 1958 a three-element gas tube, called the propagator tube, and a resistor. The semiconductor diode is normally backbiased by the applied potentials. In response to an incoming marking pulse from the terminal of the network, a marking pulse is fed through the capacitor to the starter electrode of the propagator tube. The propagator tube is ionized by this pulse and a direct current path is established between the source of potential connected to the anode and the subsequent stage of crosspoiut devices connected to the cathode of the propagator tube. A new mark signal is thereby applied to the subsequent stage of the network. By supplying current subsequent to the first stage, the propagator eliminates variations in marking voltages of the first stage and aids in supplying the current necessary to ionize an increasing number of tubes in the second and third stages. This propagator circuit requires three-element gas tubes which are relatively expensive as compared to the crosspoint type gas diodes. Accordingly, it is an object of this invention to provide an improved propagator circuit.

It is another object of this invention to provide a propagator circuit employing as its active element a crosspoint type diode.

7 It is another object of this invention to provide a propagator circuit which can be actuated only by a combination of two pulses.

In crosspoiut switching networks of these'types, the

operation is sequential, the crosspoints from the ends of the network being rendered conducting in succession. In

the operation, each crosspoiut connected betweena va-" cant output node and an input node to which a mark pulsef is applied becomes conducting so that there is a fanningout of crosspoints through which conduction exists untila unique path is established through the network. 3 After the unique path is established, the crosspoints not em-' ployed in that path will be rendered nonconducting because of a decrease in potential at the several nodes caused by a terminal-to-terminal current flow through a high valued terminal resistance and a decrease in voltage applied to the nodes as a result of a switching arrangement in the power supply. point devices, the number of stages and hence the size of the network is limited. Inthese networks, the marking potential applied to a vacant node to break down the operated in tandem. One way to improve the operating margins is to generate a new mark signal intermediate the network.

In R. W. Ketchledge application Serial No. 426,338,

filed April 29, 1954, there is disclosed a marking pulse propagator circuit interposed in a crosspoiut switching network. This circuit includes a semiconductor diode and a series circuit connected in parallel with the semi- .conductor diode.

In prior circuits employing cross:

This series circuit includes a capacitor,

. It is another object of this invention to actuate a propagator circuit for a minimum required period while insuring marking of the subsequent stage. Y In accordance with aspects of this invention, a propagatorcircuit is employed between stages of a crosspoiut network, which propagator circuit contains as its active element a crosspoiut type gas diode. diode is connected directly between the preceding and succeeding stages of the network and this semiconductor diode is connected in parallel with a series combination of condenser-resistor and gas diode. A voltage greater than a sustaining voltage is normally applied across'the propagator gas diode by a high impedance source of potential. Nonselective propagator pulses are applied to the anode of the propagator tube from a source of pulses connected to the propagator tube by a semiconductor diode. The semiconductor diode between the source of nonselective propagator marking pulses and the anode of the propagator gas diode is normally back-biased by the high impedance source connected to the anode of the gas diode. Pulses from the pulse source are of just suflicient magnitude to overcome the back-bias on this semiconductor diode but insufiicient alone to cause the gas diode to ionize. When an incoming marking pulse is received from a terminal of the network, a pulse is difierentiated by the condenser and the resistor of the high impedance source and applied to the anode of the propagator gas diode. The propagator tube will ionize as a result of this pulse alone. However, the propagator tube will be quickly extinguished by the high potential drop across the high resistance connected between the anode of the propagator diode and one source of sustain voltage unless a nonselective propagator pulse is also applied to the anode from a low impedance source to provide a path for propagator tube sustain current.

Accordingly, it is a feature of this invention to employ v a crosspoiut type diode as an active element of a propagator circuit.

It is still another feature of this invention to apply a nonselective marking pulse to the active element of the propagator circuit, which pulse in combination with the incoming marking pulse from a network terminal causes the propagator tube to deliver a new marking pulse to the subsequent crosspoiut stage.

It is another feature of this invention to apply a selec A semiconductor magnitude just suflicient to overcome the'back' bias on 10 thesemi-conductor diode andapply a sustain potential to the propagator gas diode but have insuflicienrmag'e nitude-to cause disturbing-pulses tobe introduced in the" communications path;

A complete understanding ofthis' invention and of these and various other features thereof may be gained from consideration-of i the following detailed description andthe accompanying drawing whichis a schematicrep-- resentationof a'portion .of a crosspoint switching network. including. a propagator circuit in accordance with trativeembodiment; of this invention. The crosspoint stages ofthe network. enclosed in blocks- 11 and 13 are represented as crosspoint gas diodes. The crosspoint-1 diodes .may be ofthe types: disclosed in applications Serial No.- 169;121;.filed-June 20, 1950-of-M. A. Townsend, nowi 533,671, filed May 9,1956 of A. D. White; and Serial No; 583,665, filedMay 9,.1956015 R. L.-Mueller and. W. G. Stieritz. These gaseous diodes are characterized by-havinga'negative resistance characteristic in the currentand frequency ranges of operation in the network.

Block.,12gis-interposed between these two stages of crosspoints, and; contains .two propagator circiuts. Numerals 20, and-.22'designate'two nodes in the network. Semiconductor; diodej 23; is serially connected between gas diodesof the prior crosspoint'stage containedin-block 11" aud gas diodesof thejsubsequenhcrosspoint stage contained in .block. 13.- Diode 23 is normally maintained in aback-biasedcondition by applied potentials as will be subsequently explained; A- series circuit is connected" in parallel with -diode 23, which series circuit includes resistorv 24,.capflcitor 25131111 crosspoint type diode 26. Wliilepropagator diode 26-maybeidentical in electrode: structure to the crosspoint gas diodes, diode 26 may'advantageouslyvhave agreater gas pressure than the crosspoint diodes thereby permitting the propagator gas diodes to supply large amounts of currents to an increasing'number of crosspoint diodes ,in the subsequent stages of the. network. A.source 23 of potential is connected through. resistor 27-to the input side of'the propagator circuit and assists, in applying a back-bias to diode 23, as, wellas 5 maintainingan idle potential across thefirst stage. of: crosspoints. Diode 29 -is connected between low impedance source 3001? nonselective-propagator markpulses' and the anode of propagator-tube 26. Diode 29 is'nor mallymaintained in a back-biased condition by a source;

intermediate diode 29 and tube26.-

Resistor 32 and capacitor25 form a difierentiatingcir cuit for the incoming marking pulses and in response to:

31.0fpotential connected .through resistor 3210a point.

a marking pulse apply a, sharp ionizing pulse of increased; 6

magnitude to the anode of tube 26. Resistor 32;.also serves to present a high impedance. to the-sustain currentg for diode 26 'when the sustain current is rnomentarily;

suppliedby source 31. Resistor 2.4 impedes the discharge of capacitor 25into tube 26. and-.thus.controls\the durar;

tion of the ionizingpulse. Diode. 33 is COIIHECted tOxIhB-J'E gator to the subsequent stage of crosspoint devices. Re-

' sistot 35'is'connected betWeen a source 36 ofnegative potential and the crosspoints of the subsequent stage to maintain an idle potential across these crosspoints. T1118 idle potential may be greater than the sustaining poten tial of the crosspoint devices and resistor 35 may be a high resistance to assure deionization of crosspoint devices not in: the singlerror. unitary selected paththrough the switching network, as disclosed in application Serial No.

6175087, filed October 19,- 1956- of K. S; Dunlap or" resistance 35" maybe a low value of resistance and the potential of'source 30*may be of theorder of the sustain voltage, in which case node marking and disconnect switches may-be employed, asis: known in the art and disclosed in the above-mentioned Bruce-Straube patent. Tube 26 is maintained above the sustain potential by sources 31 and 36. However, resistor 35 is qiute large, for example, 2 megohms, and when the sustain current fortube 26 flowsthrough resistor 35, it causes alarge potential drop;- Tliis potential drop' causes tube 26-to deionize after the nonselective' propagator pulse is terminated.

Assume now for tlie-purposes of. explanation of the operation-=ofi the= circuit depicted in the drawing that there are no priorly establishedcallsthrough the network and that-fia path-is to be established between nodes 20-and225; Otrthebasis of these assumptions, marking pulses are applied to nod'es 20 and 22. These marking pulse's -may be' applied by the ionization ofprior stages Patent 2,804,565 issued August 27; 1957; Serial No. 30

of the network or byother propagators. The pulses appliedito node 20 in comb'ination-withthe negative voltagemornrallyt applied to the' opposite side of stage- 11 cause; all: of the tubes in stage 11-, connected between node-1211 andithe'nodeswhichare-idle, such as diode 21,

Intresponse to the ionization of diode 21;.

tom-b e; ionized; a: positive: :pulseis applied to diode 23 and capacitor 25.- Sinceediode 23.is. back-biased, thispulse is differentiated by; the; combination of capacitor 25- and'resistor 32 and applied to the: anode of diode 26 causing diode 26 to ionize;:;.,Resisto'r 24 impedesthedischarge of capacitor 25. togprevent excessive. current from flowing through diode; 26. This: resistor. also. assures that the pulse will beaapplied for. a suflicient-v time to insure ionization onmarking; of .diode 26; Similarly, all propagator diodes 26.'connec-tc d through ionizedicrosspoints to node 20 and: also.-connectedto.=an idle node; such as node 38 -will be ionized. While-diode 26 is. thus :ionized, a nonselective pulse is; applied'from' pulse source 30 which presents aulow impedance sourceof sustaining voltage to diode 26.

The-sustaining current for diode 26 is therefore supplied through diode 29-from low impedance source. 30.

Inthe absence of the marking. pulse. from node 20, pulses from nonselective pulse source 30 just overcome the back-bias on .diode 29 butare not sulficient to causeiouizationofrtubie 26. If di'ode 29rwere not'back-biased, the nonselective pulses from pulse.source.30 -wouldin-' troduce noise. into the;network. This noise would be objectionable in. propagator; circuits connected to es-- tablished pathslthrough the. network. Since the pulses frornpulse source. 30 donot introduce disturbing pulses to.establish paths andsince they are: insufiicient alone' tocause ionization of propagator tubes 26, these pulsesmay. be, continuou-sly' applied. However, .pulse source 30 maybe actuated :only in response to the application of-a' marking; pulse. atav network terminal as disclosed in application .Serial'No. 617,131, filed October 19, 1956, by: G. E. Jacoby; and J. W. Rieke.

The ionization of tube -26 effectively closes the circuit between pulse source 30 and subsequent stage1-3 deliver ing a,-new marking, pulse to this stage. This marking pulseionizes .all-tcrosspoints. of subsequent stage 13 con-- nected :to node 38,. for example diodes .391 and 40. This new 'pulse: is limited-in magnitude by clamping diode 33, which diodezfis controlled by source 34. The marking and;breakdown (sf-"subsequent'stage 13 causes a drop in potential of the node 3Q and diode 23 becomes forwardly biased thereby presenting a low impedance path to the communications currents. The ionization of diode 39 establishes a communications path between nodes 20 and 22. After the unique path'is established through the remainder of the distribution network (not shown), terminal and node voltages may be decreased to the sustaining voltage by any convenient means, causing the crosspoints in the unselected paths, such as diode 40, to be extinguished.

Reference is made to application Serial No. 617,189, filed October 19, 1956, of R. W. Ketchledge wherein a related invention is disclosed and claimed and wherein the incorporation of propagator circuits in accordance with this invention into crosspoint switching networks is more fully disclosed.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A circuit for generating a new marking signal in a crosspoint switching network including a semiconductor diode serially connected between adjacent stages of crosspoints, a condenser and a gas diode connected in parallel with said semiconductor diode, means for applying a :tirst pulse to said condenser and said semiconductor diode, means maintaining a sustaining potential across said gas diode and means for applying a second pulse to said gas diode whereby said first pulse ionizes said gas diode and said second pulse sustains said gas diode thereby applying a new marking pulse to said crosspoint switching network.

2. A propagator circuit between two stages of a crosspoint communications switching network including a condenser and a gas diode connected in series between said stages, a first semiconductor diode connected between said stages and in parallel with said condenser-gas diode circuit, a source of nonselective propagator marking pulses, a second semiconductor diode connected between said source and said gas diode, means normally maintaining said second semiconductor diode back-biased, means including one of said stages for marking said gas diode and means includingsaid source of nonselective pulses for sustaining said gas diode whereby said gas diode generates a new marking signal for one of said stages in response to a marking pulse from another of said stages and a pulse from said pulse source.

3. A propagator circuit for generating a new marking signal in a crosspoint switching network of gaseous discharge devices arranged in stages including a semi-conductor diode serially connected between adjacent stages of said network, means normally maintaining said semiconductor in a back-biased condition, a gas diode connected to one side of said semiconductor diode, a difierentiating circuit connected to the other side of said semiconductor diode and to said gas diode, means including the preceding stage of said crosspoint devices and said diiferentiating circuit for ionizing said gas diode, and pulse means for sustaining said gas diode whereby a new mark pulse is generated and transmitted to the subsequent stage crosspoint devices in response to the sustaining current flowing through said gas diode.

4. A propagator circuit for generating a new marking signal in a crosspoint switching network including a semiconductor diode serially connected between adjacent stages of crosspoints, a serially connected condenser and gas diode connected in parallel with said semiconductor diode, means for applying a marking first pulse to said condenser and said semiconductor diode and means for applying a sustaining second pulse to said gas diode whereby said first pulse ionizes said gas diode and said second pulse sustains said gas diode and applies a new marking pulse to points.

5. A propagator circuit for generating a new marking signal in a crosspoint switching network including a semiconductor diode serially connected between adjacent said semiconductor diode, high impedance means maintaining a sustaining potential across said gas diode and low impedance means for applying a second pulse to said gas diode whereby said first pulse ionizes said gas diode and said second pulse sustains said gas diode thereby applying a new marking pulse to said crosspoint switching network.

6. A propagator circuit connected between two stages of a communications switching network comprising stages of crosspoints including a semiconductor diode, means normally maintaining said semiconductor diode in a back-biased condition, gas diode means connected to one side of said semiconductor diode, a difierentiating circuit connected to the other side of said semiconductor diode and to said gas diode means, means including the preceding stage of said crosspoint devices and said difierentiating circuit for applying a marking pulse to said gas diode, said marking pulse being of sutlicient magnitude to ionize but of insutficient duration to sustain said gas diode, and non-selective pulse means for applying a pulse to said diode, said last-mentioned pulse being of suflicient magnitude and duration to sustain said gas diode for a period suflicient to insure marking of the crosspoint devices in the subsequent stage of crosspoints connected to said propagator circuit.

7. A propagator circuit for generating a new marking signal in a switching network having crosspoint stages of gaseous discharge devices including a semiconductor diode serially connected between adjacent stages of said network, gas diode means connected to one side of-said semiconductor diode, said gas diode having the same electrode structure as said gaseous discharge devices but having a greater gas pressure than said gaseous discharge devices, a difierentiating circuit connected to the other side of said semiconductor diode and to said gas diode, means including said differentiating circuit for ionizing said gas diode, and pulse means for sustaining said gas diode whereby a new mark pulse is applied to the subsequent stage of crosspoint devices in response to the sustaining current flowing through said gas diode.

8. A propagator circuit for a crosspoint switching network comprising a first semiconductor diode connected between a preceding and a succeeding stage of the switching network, means for normally back-biasing said first' semiconductor diode, a condenser, resistor, and gaseous diode connected in parallel across said semiconductor diode, a second semiconductor diode connected to said gaseous diode remote from said first semiconductor diode, means connected to said second semiconductor diode and to said gaseous diode for maintaining said second semiconductor diode normally back-biased, and means for applying a voltage pulse to said second semiconductor diode to render said second semiconductor diode conducting and establish thereby a low impedance I sustaining path for said gaseous diode.

9. A propagator circuit in accordance with claim 8 wherein the cathode of said gaseous diode is connected to said first semiconductor diode and the anode of said gaseous diode is connected to said second semiconductor diode.

10. A propagator circuit for a crosspoint switching network comprising a first semiconductor diode serially connected between adjacent stages of the network, means normally maintaining said first semiconductor diode backbiased, a gas diode connected to one side of said first semiconductor diode, a differentiating circuit connected one of said dicelit stages of crss to the other-side. of said first semiconductor diode and to semiconductor diode'conducting and establish thereby. a said gas diode, means including the preceding stage of low impedance sustaining path forsaid'gas diode.

the network and said diiferentiating circuit for ionizing v H 1 said gas -diode, a second- "semiconductor diode connected ReferVemeS 'Cited'fiiftm file f 'l i p tent to said gas diode, highimpedance means connected to 5 g l I h I if i saidv gas diode and saidsecond semiconductor diode to UNITED'STATES" PATENTS I maintain a sustainingpotential across said gasdiode and 2,722,567 Davison etral Nov. 1,1955 maintainsaid second semiconductor diode normally back- 2,779,822 Ketchledge J an. .29, 1957 biased, and low .impedance means for applying a pulse 2,780,674- Sixet a1.- Feb. 5, 1957 tosaid second semiconductor diode to render said second 10- a